That still has not stopped Senate majority leader Harry Reid (D) of Nevada from trying to keep alive efforts to bring an immigration overhaul to a vote this year. Senate Democrats unveiled a new proposal for reform late last week, stressing security first, then a pathway to legalization for the estimated 10.8 million people in the country illegally. The Democrats were making a long-shot effort to attract Republican support, but none was forthcoming, and the issue has receded in Washington as the Gulf of Mexico oil slick and the failed Times Square car bomb attack consume attention.

But for Senator Reid, immigration remains a top political concern: He is embroiled in a tough reelection battle, and he needs the support of Nevada's large Hispanic population – 20 percent of the state.

Arizona's tough new anti-illegal immigration law – which requires police officers to check a person's immigration status if there is "reasonable suspicion" that the person is in the United States illegally – has added urgency to the calls for federal reform.

Critics, including President Obama, fear the law could lead to racial profiling. But the president sounds doubtful that a comprehensive reform that addresses both border security and a pathway to citizenship for illegal immigrants can be finished this year.

"We've gone through a very tough year, and I've been working Congress pretty hard," Mr. Obama told reporters on Air Force One April 28. "So I know there may not be an appetite immediately to dive into another controversial issue."

Why has fixing an immigration system widely seen as broken been so hard to achieve?

In some ways, analysts say, it's like health-care reform. There are many elements and constituencies, with well-drawn battle lines. After the Immigration Reform and Control Act of 1986 failed to deliver on its promise, a loss of trust ensued, making subsequent reform even more difficult to pursue. And as with health reform, it will take major presidential and congressional muscle to achieve success.

"People who are close to the immigrant experience feel a sense of outrage that most Americans don't understand that most immigrants are really good people who work really hard and really want to be American," Mr. Sharry adds. "On the other side, there are people who feel really strongly and outraged. They feel the country, its sovereignty, and its culture are threatened by immigration in general and in particular, illegal immigration."

Then there's the vast, ambivalent middle, and an immigration policy that is not well understood. The 1986 reform outlawed the hiring of illegal immigrants, and required employers to check job applicants for proof of legal status. But fake identification was easy to obtain, and the hiring of illegal immigrants continued apace.

Poorly guarded borders and lax enforcement of immigration laws have made it easy for illegal immigrants – many of whom arrive with visas, which they then overstay – to work their way into American life with impunity. The 1986 amnesty for some has only encouraged more to come. And the system for legal immigration was not reformed.

Complicating matters for advocates of a crackdown on illegal immigration is the opposition they face from powerful interests like the US Chamber of Commerce and labor unions, which believe immigration reform will make for a more orderly employment system and thus be a boon to the US economy.

Opponents of comprehensive reform, particularly the path to citizenship, see other motivations at work.

"This is an issue with strange dynamics," says Dan Stein, president of the Federation for American Immigration Reform. "You have well-moneyed special interests either on the side of the status quo or large-scale immigration.... Some business groups like hiring illegal labor, because it's docile and exploitable."

"More recently," Mr. Stein adds, "the Democratic Party has become more enchanted with immigration's potential to build an electoral base. The institutional interests of the two parties have hardened in a way that neutralizes positive public discourse."

In the run-up to the 2010 midterms, the importance of the Latino vote is evident.

In a February report, America's Voice identifies 40 battleground House and Senate races where Latino voters will be key. Although immigration is not the No. 1 issue for most Latinos, it is "clearly a defining issue," the report says.

"Like all Americans, the economic crisis continues to be the biggest concern for Latino voters," the report continues. "However, their closeness to the immigrant experience makes immigration reform a threshold issue for many."

So it's not just Reid who is looking to his Latino constituents to save his seat.

But on the flip side, there are members for whom the immigration issue could be toxic, particularly so for conservative Democrats in districts without large immigrant populations. They want nothing to do with immigration reform this year.

The Arizona law goes into effect 90 days from its April 23 signing, unless a court challenge succeeds in blocking implementation.

The most likely outcome for immigration reform is that the Senate holds off at least until next year, allowing the electoral considerations to recede in prominence.

But one need look no further than the major push for immigration reform in 2007 to wonder if an overhaul will ever be doable.

Then, a Republican president, George W. Bush, led the charge and got 12 Republican senators to join him, but the measure still failed to reach the floor for a vote.

In this latest effort at reform, the only Republican willing to work with the Democrats was Sen. Lindsey Graham (R) of South Carolina. Now he's off that track, incensed that Reid had pushed to move immigration reform before energy legislation – and, some analysts say, to protect his friend John McCain, the Arizona senator who at one time was a major proponent of comprehensive reform but has backed away, given his primary challenge from the right.

"What you have is great disappointment that immigration didn't move in 2007, despite bipartisan support, a Republican president pushing it, and things getting a lot worse out there with laws like in Arizona," says Democratic communications strategist Peter Fenn. "There is impetus to move solid, good federal legislation, especially when states are going to blame the federal government for not acting. But the key is to craft a bill that can actually pass."